replacement spark plug-rethreading

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OLDSCOT

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Jun 19, 2009
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Had some problems with my recently purchased 2 stroke kit..Removed the plug to determine its condition and noticed that several of the threads in the head were stripped -also noted that the spark plug threads of the Chinese plug were not as protruding as those on an US plug.
Two questions- Is there an US replacement plug(long threads) that is compatible with the Chinese plug? Due to to the stripped threads,will have to install a helicoil or similar insert
in the head. Has anyone every done this and what is the procedure. Have notified the supplier and hope that they will supply a new head and a new plug but we all know how that goes.
Thanks
 
Kevlarr

Kevlarr

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Jul 22, 2009
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Regular spark plug threads can be 7/8"-18, M10-100, M12-125, M14-125 and M18-150.
 
Humsuckler

Humsuckler

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Jul 28, 2009
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there is a special tool out there for us engine builders called a thread chaser, it has a magnetic tip on it that will collect the chips on its way up.
its a must have!
 
Kevlarr

Kevlarr

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Humsuckler said:
there is a special tool out there for us engine builders called a thread chaser, it has a magnetic tip on it that will collect the chips on its way up.
its a must have!
Click to expand...
That only works on iron heads not aluminum. It's a good practice no matter what the material the head is made from to coat the tap with a liberal amount of grease to collect the shavings.
 
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restapukin

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Jul 22, 2009
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I haven't done any helicoiling for years, but, what fantastic technology!

do not pass go; move directly to a helicoil kit; it's easy to do, and gives a superb result ... a result that improves upon a virgin head...

in fact.

You'll love helicoils.
 
GearNut

GearNut

Active Member
Aug 19, 2009
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I have had waaay too many heli-coils unscrew with the fastener.
Now given I did not install them, I do not know if they were incorrectly installed.
I greatly favor time serts. Properly installed they will never come out.
Antique Volkswagen and dune buggy afficinados will know them as case savers. They are commonly used in the avaition industry as well.
They are a hardened tool steel cylinder with the threads you want on the inside and special threads on the outside.
They install similar to a heli-coil, but not quite.
Due to the cost of a kit, it would be best to have a machine shop or engine repair shop install it.
The actual insert is only about $5.00 US, but the special tools are pricy.
 
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restapukin

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Jul 22, 2009
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ok, when I say I haven't used helicoils for years I was being economical with the truth. I'll make a clean breast of it... I haven't used helicoils for decades ... & more like four than three. You used to be able to get spark-thread kits with all the tooling included. Once upon a time.

I have never come across time serts; they sound great.

But helicoils have always behaved themselves for me, so my liking for them is undiminished. They end up locked in place through cunning mechanical precision keying, backed up with some super-loctite gunk, don't they?

roflmao ... I suppose i'm gonna hafta go google myself up-to-date on helicoil kit pricing now.
 
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chrisme

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May 30, 2009
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I have never done a heli-coil on an HT engine, but I had to do one on my subaru because when I was replacing a plug it was bound to the head and pulled the threads out with the plug.
They make a special kit for plugs. And I didn't even have to take the head off my subaru. (which is a good thing because it is a major PITA on a boxer engine...)
 
floridaboy

floridaboy

Member
Apr 25, 2009
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Hudson, FL.
You should call the dealer that you got the engine from and tell him about the bad head and see if he will send a new one. The replacement heads can be found from dealers on the site and are around $12.00. That will be cheaper then trying to fix what you have. When you get it all fixed remember to NEVER remove a spark plug when engine is still hot it will strip out the threads. When installing new NGK or any new plug use ANTI-SEIZE on the threads. Hopes this helps.
 
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chrisme

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May 30, 2009
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Maine
+1
I think a heli-coil costs about $12. But if you went that route you'd never have to worry about threads again.
 
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restapukin

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Jul 22, 2009
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chrisme said:
+1
I think a heli-coil costs about $12. But if you went that route you'd never have to worry about threads again.
Click to expand...
so; a brand new head for $12 versus your own tried and tested head - helicoil FIXED for $12

gimme my own tried and tested head with the equally tried and tested helicoil solution for the $12

simply better ... but I've always liked helicoils....
 
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chrisme

New Member
May 30, 2009
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Maine
restapukin said:
so; a brand new head for $12 versus your own tried and tested head - helicoil FIXED for $12

gimme my own tried and tested head with the equally tried and tested helicoil solution for the $12

simply better ... but I've always liked helicoils....
Click to expand...
Some people say they leak when used for spark plugs, but I've had one in my car for over 10,000 miles, and not one issue.
 
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